CN112970081A

CN112970081A - Method for producing sintered magnet and sintered magnet

Info

Publication number: CN112970081A
Application number: CN202080006088.1A
Authority: CN
Inventors: 成乐宪; 金仁圭; 权纯在; 催晋赫; 鱼贤洙; 金太勋
Original assignee: LG Chem Ltd
Current assignee: LG Chem Ltd
Priority date: 2019-09-26
Filing date: 2020-09-24
Publication date: 2021-06-15
Anticipated expiration: 2040-09-24
Also published as: KR102589893B1; KR20210036824A; EP3855459A4; CN112970081B; US20210398718A1; JP7158807B2; EP3855459A1; EP3855459B1; JP2022511483A

Abstract

The present disclosure relates to a method for producing a sintered magnet and a sintered magnet produced thereby, and the method for producing a sintered magnet includes the steps of: producing an R-Fe-B based magnet powder by a reduction-diffusion method, adding an R-Al-Cu powder as a sintering agent to the R-Fe-B based magnet powder to form a mixed powder, and sintering the mixed powder to form a sintered magnet, wherein the R-Al-Cu powder is an alloy of R, A1 and Cu, and R is Nd, Pr, Dy, Tb, or Ce.

Description

Method for producing sintered magnet and sintered magnet

Technical Field

Cross Reference to Related Applications

This application claims the benefits of korean patent application No. 10-2019-0118839, filed at 26.9.2019 and korean patent application No. 10-2020-0122724, filed at 23.9.2020 and each of which is incorporated herein by reference in its entirety.

The present disclosure relates to a method for producing a sintered magnet and a sintered magnet produced thereby. More particularly, the present disclosure relates to a method for producing a sintered magnet using a sintering agent to improve magnetic characteristics and a sintered magnet produced by the method.

Background

The NdFeB-based magnet has Nd₂Fe₁₄A permanent magnet of the composition of B, which is a rare earth element of neodymium (Nd), and a compound of iron and boron (B), and has been used as a general permanent magnet for 30 years since its development in 1983. NdFeB-based magnets are used in various fields, such as electronic information, automotive industry, medical equipment, energy sources, and transportation. In particular, in line with recent trends toward weight reduction and miniaturization, NdFeB-based magnets are used in products such as machine tools, electronic information devices, electronic products for home appliances, mobile phones, robot motors, wind power generators, small motors for automobiles, and driving motors.

For the general production of NdFeB-based magnets, strip casting/die casting or melt spinning methods based on metal powder metallurgy are known. First, the belt casting/die casting method is a method of: in which a metal such as neodymium (Nd), iron (Fe), boron (B) is melted by heating to produce an ingot, and the grain particles are coarsely pulverized and subjected to a miniaturization process to produce fine particles. These steps are repeated to obtain a magnet powder, and the magnet powder is subjected to a pressing and sintering process under a magnetic field to produce an anisotropic sintered magnet.

Further, the melt spinning method is a method of: in which a metal element is melted, then poured into a wheel rotating at a high speed, rapidly cooled, pulverized by a jet mill, and then blended with a polymer to form a bonded magnet, or pressed to produce a magnet.

However, all of these methods have the following problems: a pulverization process is basically required, a long time is spent in the pulverization process, and a process of coating the surface of the powder is required after the pulverization. Furthermore, due to the existing Nd₂Fe₁₄The B particles are produced by the following method: in which a raw material (1500 to 2000 ℃) is melted and quenched, and the obtained block is subjected to a multi-step process of coarse pulverization and hydrogen crushing/jet milling, so that the particle shape is irregular and there is a limit to miniaturization of the particles.

Recently, a method for producing magnet powder by a reduction-diffusion method has been attracting attention. For example, uniform fine NdFeB particles in which Nd is incorporated can be produced by a reduction-diffusion method₂O₃Fe and B are mixed and reduced with Ca or the like. However, in this method, an oxide film may be formed during the removal of the reducing agent used at the time of reduction, such as Ca, and the reduction by-products. The oxide film makes it difficult to sinter the magnetic powder, and the high oxygen content promotes decomposition of the columnar magnetic particles, and may deteriorate the characteristics of a sintered magnet obtained by sintering the magnetic powder.

Disclosure of Invention

Technical problem

Embodiments of the present disclosure are designed to solve the above-mentioned problems, and an object of the present disclosure is to provide a method for producing a sintered magnet, which improves characteristics of the sintered magnet by adjusting phases distributed in grain boundaries during sintering of magnetic powder, and a sintered magnet produced by the method.

However, the problems to be solved by the embodiments of the present disclosure are not limited to the above-described problems, and various extensions may be made within the scope of the technical ideas included in the present disclosure.

Technical scheme

A method for producing a sintered magnet according to one embodiment of the present disclosure includes the steps of: producing an R-Fe-B based magnet powder by a reduction-diffusion method, adding an R-Al-Cu powder as a sintering agent to the R-Fe-B based magnet powder to form a mixed powder, and sintering the mixed powder to form a sintered magnet, wherein the R-Al-Cu powder is an alloy of R, A1 and Cu, and R is Nd, Pr, Dy, Tb, or Ce.

The method for producing a sintered magnet may further include the step of forming an R-Al-Cu powder as a sintering agent, wherein the step of forming the R-Al-Cu powder may include the steps of: mixing RH with water₂The method includes mixing a powder, an Al powder, and a Cu powder to form a sintering precursor, agglomerating the sintering precursor, increasing a temperature of the agglomerated sintering precursor to form a metal alloy, and pulverizing the metal alloy to form a sintering agent.

The method for producing a sintered magnet may further include the step of wrapping the sintered precursor in a metal foil while raising the temperature of the agglomerated sintered precursor.

The step of forming the sintering precursor may further comprise the step of mixing the liquid Ga.

The metal foil may be Mo or Ta.

When the agglomerated sintering precursor is wrapped in a metal foil and the temperature is raised, the temperature may be raised in an argon atmosphere.

The step of forming the metal alloy may further comprise the steps of: the agglomerated sintering precursor is wrapped in a metal foil, the temperature is raised to 900 to 1050 degrees celsius, and then additional heat treatment is performed.

The step of agglomerating the sintering precursor may use any one of hydraulic Pressing, tapping (tapping), and Cold Isostatic Pressing (CIP).

The method for producing a sintered magnet may further include adding NdH to the R-Al-Cu powder as a sintering agent₂And (5) powder preparation.

A sintered magnet according to another embodiment of the present disclosure is produced by the production method described above.

Advantageous effects

According to the embodiment, in order to prevent the characteristics of the sintered magnet from being deteriorated due to the oxide film generated when the magnetic powder is produced as in the related art, the metal alloy powder may be used as a sintering agent, thereby preventing the characteristics of the sintered magnet from being deteriorated while lowering the melting temperature.

Drawings

Fig. 1 is a view showing a step of producing R-Al-Cu metal alloy powder in a method of producing a sintered magnet according to one embodiment of the present disclosure.

Fig. 2 is a BH graph showing magnetic flux density (Y-axis) according to coercive force (X-axis) measured in sintered magnets produced according to comparative examples and examples of the present disclosure.

Fig. 3 is a BH graph showing the magnetic flux density (Y-axis) according to the coercive force (X-axis) measured in the sintered magnets produced according to the comparative examples and examples of the present disclosure when the composition of the magnetic powder was changed before sintering of fig. 2.

Fig. 4 is a BH graph showing magnetic flux density (Y-axis) according to coercive force (X-axis) measured in a sintered magnet produced by changing the type of rare earth metal contained in a metal alloy when a metal alloy powder according to one embodiment of the present disclosure is used as a sintering agent.

Fig. 5 and 6 are graphs showing magnetic flux densities (Y-axis) according to coercive force (X-axis) measured before and after using a quaternary metal alloy powder as an adjuvant for infiltration sintering of a magnet.

Detailed Description

Hereinafter, various embodiments of the present disclosure will be described in detail so that those skilled in the art can easily implement them. The present disclosure may be modified in various different ways, and is not limited to the embodiments set forth herein.

Further, throughout the specification, when a portion is referred to as "comprising" a certain component, it means that the portion may further comprise other components without excluding other components, unless otherwise specified.

According to the present embodiment, the magnetic powder can be produced by a reduction-diffusion method using a low-cost rare earth oxide. In such a method, an oxide film may be formed during the removal of a reducing agent such as Ca used in reduction and a reduction by-product. Such an oxide film makes it difficult to sinter the magnetic powder and may impair the characteristics of the sintered magnet. To complement this, the present embodiment uses metal alloy powder as a sintering agent, so that it is possible to prevent the characteristics of the sintered magnet from deteriorating while lowering the melting temperature.

When the oxygen content inside the magnet powder increases during sintering, the magnetic characteristics deteriorate, and therefore it is necessary to use a high-purity metal alloy. However, to produce such alloys, it is often necessary to subject the metal pieces to arc melting or induction melting to cause them to melt at high temperatures. For example, in the case of the arc melting method, such a process may be repeated: wherein the molten metal pieces are turned over and remelted by melting the pieces together in a vacuum atmosphere at about 2000 to 3000 degrees celsius by generating an arc through high voltage and high current. However, due to the space limitations of the arc melter and the limitations of the maximum amount of sample for uniform melting, the alloy can only be produced in small quantities. In addition, it is difficult to precisely control the temperature during the arc melting process, and in the case of aluminum, aluminum is vaporized and causes loss during melting due to vapor pressure in vacuum, thereby making it difficult to add a precise ratio.

On the other hand, according to the present embodiment, when the melting temperature is lowered during production of the metal alloy used as the sintering agent, the cost can be reduced. In particular, according to the present embodiment, since the RH is applied₂Powder and respective metal powderWhile sintering agents are produced at less than 1050 degrees celsius, so that economic efficiency can be improved at this stage of the process. Further, in the case of a metallic material that is liquid at room temperature such as Ga, if arc melting is used, it disperses during arc formation, which is technically difficult to manufacture an alloy, and according to the present embodiment, an accurate ratio can be added.

In the present embodiment, the metal alloy as the sintering agent corresponds to the following case: 1) a case where each metal powder corresponding to each element constituting the alloy is contained as a sintering agent, or 2) a case where a material corresponding to each element constituting the alloy is prepared as a precursor before sintering and a metal alloy powder is contained as a sintering agent.

According to one embodiment of the present disclosure corresponding to case 2) above, it includes a step of adding R-Al-Cu metal alloy powder as a sintering agent to R-Fe-B based magnet powder to form mixed powder. Specifically, the step of forming the R-Al-Cu powder includes the steps of: mixing RH with water₂The method includes mixing a powder, an Al powder, and a Cu powder to form a sintering precursor, agglomerating the sintering precursor, wrapping the agglomerated sintering precursor in a metal foil and raising a temperature to form a metal alloy, and comminuting the metal alloy to form a sintering agent. The step of forming the sintering precursor may further comprise the step of mixing the liquid Ga. Further, the metal foil may include Mo or Ta.

Referring to FIG. 1, RH may be mixed therein₂The sintered precursors of the powder, Al powder and Cu powder are compressed by Cold Isostatic Pressing (CIP) or the like, and the block may be wrapped in a metal foil of Mo or Ta. The block 300 wrapped in the metal foil is placed in an alumina crucible 100 and heated to about 1050 degrees celsius under an argon (Ar) atmosphere in a tube furnace 200, thereby obtaining a high purity alloy. At this time, the tube furnace 200 may be formed of a material such as alumina or SUS (stainless steel).

According to the present embodiment, it is advantageous to produce a large amount of metal alloy without space limitation, and a material that is easily vaporized (e.g., aluminum) is also vaporized at a high temperature to minimize a loss part, so that an accurate addition ratio can be adjusted in progress of the process. Further, since an electric furnace such as a tube furnace, which can accurately control the temperature and control the gas atmosphere during the process, is used, a relatively low-cost apparatus can be used. Further, not only an element that evaporates well, such as aluminum, but also a metal material that is liquid at room temperature, such as Ga, can be added in a precise ratio. Further, the use of a vacuum state is not required, and the metal alloy can be simply produced at normal pressure.

The forming of the metal alloy may further comprise the steps of: the agglomerated sintering precursor is wrapped in a metal foil, the temperature is raised to 900 to 1050 degrees celsius, and then additional heat treatment is performed. Here, the additional heat treatment is a heat treatment at a relatively low temperature of the already synthesized alloy, and a more uniform phase can be obtained by such annealing.

The step of agglomerating the sintering precursor may be performed using any one of hydraulic pressing, tapping and Cold Isostatic Pressing (CIP) methods.

May further comprise adding NdH to the R-Al-Cu powder as a sintering agent₂And (5) powder preparation. Since sintering of the magnet powder itself is impossible, NdH contained in the sintering agent₂The powder is made to pass through with a small amount of NdH₂The magnetic powder is sintered by mixing the powders.

Since R (rare earth) is mixed with Cu at a ratio of about 7:3_0.7Al_0.2Cu_0.1Since the composition (2) generally has the lowest melting point, it is preferable to set R to 0.7. According to the present embodiment, from a composition of 100% Al and 0% Cu to a composition of 50% Al and 50% Cu, which are melted together at less than 800 degrees celsius to form an alloy, where Al may be prepared with a composition greater than that of Cu. If a large amount of Al and Cu is added as a sintering agent, the magnetic flux density may decrease.Therefore, at the time of sintering, 0.17 wt% of Al and 0.2 wt% of Cu were added, and NdH was further added₂To set a reference value, and then sintering is performed.

Hereinafter, a method of producing a sintered magnet according to one embodiment of the present disclosure will be described in more detail. However, the following embodiments correspond to the embodiments for explaining the present disclosure, and the scope of the present disclosure is not limited thereto.

Comparative example 1

Will be Nd_2.4Fe_12.8BCu_0.05The synthesized magnetic powder and sintering agent were mixed in a mortar, and the mixture was placed in a molybdenum (Mo) crucible or a carbon (C) crucible as a mold to obtain a magnet of a desired shape. Thereafter, at about 10^-6The temperature is raised to 850 degrees celsius at a ramp rate of 300 degrees celsius/hour in an ultra-high vacuum state of torr or less, and then maintained for about 30 minutes. The temperature was again raised to 1070 degrees celsius at the same temperature raising rate, held for two hours, and then naturally cooled to room temperature to obtain a sintered body (material after sintering). During the sintering process, 6 wt.% NdH was added₂As a sintering agent. All operations were performed in an argon (Ar) atmosphere.

Example 1

Sintering was carried out under substantially the same conditions as in comparative example 1, except that 6% by weight of NdH was added during the sintering₂Powder, 0.17 wt% Al powder and 0.2 wt% Cu powder as sintering agents.

Example 2

Sintering was carried out under substantially the same conditions as in comparative example 1, except that NdH was added during the sintering₂And Nd_0.7Al_0.2Cu_0.1As a sintering agent so that the amount is the same as that of example 1. In other words, when the mixtures of the magnet powder and the sintering agent in examples 1 and 2 were sintered, the atomic weight ratio of each added metal element with respect to the mass of the magnet powder may be the same.

To prepare NdH₂And Nd_0.7Al_0.2Cu_0.1The metal alloy powder of (4), using the following method for producing a sintering agent. Mixing NdH₂The powder, Al powder and Cu powder were mixed and the mixture was agglomerated by Cold Isostatic Pressing (CIP). Thereafter, the agglomerated mixture was wrapped in Mo metal foil or Ta metal foil, heated to 300 degrees celsius for 1 hour in an argon (Ar) gas atmosphere, and further heated at 900 degrees celsius to 1050 degrees celsius for another 1 hour. The prepared metal alloy is pulverized to obtain a powder form.

Comparative example 2

Sintering was carried out under substantially the same conditions as in comparative example 1, except that Nd was used_2.4Fe₁₂Co_0.8BCu_0.05Composition of (3) instead of Nd_2.4Fe_12.8BCu_0.05The composition (a) is a synthetic magnetic powder. Furthermore, 10% by weight of NdH was added₂As a sintering agent.

Example 3

Sintering was carried out under substantially the same conditions as in comparative example 2, except that 10% by weight of NdH was added during the sintering₂Powder, 0.17 wt% Al powder and 0.2 wt% Cu powder as sintering agents.

Example 4

Sintering was carried out under substantially the same conditions as in example 3, except that NdH was added during the sintering₂And Nd_0.7Al_0.2Cu_0.1As a sintering agent so that the amount is the same as that of example 3. To prepare NdH₂And Nd_0.7Al_0.2Cu_0.1The metal alloy powder of (4), using the following method for producing a sintering agent. Mixing NdH₂The powder, Al powder and Cu powder were mixed and the mixture was agglomerated by Cold Isostatic Pressing (CIP). Thereafter, the agglomerated mixture was wrapped in Mo metal foil or Ta metal foil, heated to 300 degrees celsius for 1 hour in an argon (Ar) gas atmosphere, and further heated at 900 degrees celsius to 1050 degrees celsius for another 1 hour. Will be provided withThe prepared metal alloy is pulverized to obtain a powder form.

Example 5

Sintering was carried out under substantially the same conditions as in example 4, but with NdH₂And Dy_0.7Al_0.2Cu_0.1As sintering agent instead of NdH₂And Nd_0.7Al_0.2Cu_0.1The alloy powder of (4).

Example 6

Sintering was carried out under substantially the same conditions as in example 4, but with NdH₂And Pr_0.7Al_0.2Cu_0.1As sintering agent instead of NdH₂And Nd_0.7Al_0.2Cu_0.1The alloy powder of (4).

Fig. 2 is a BH graph showing magnetic flux density (Y-axis) according to coercive force (X-axis) measured in sintered magnets prepared according to comparative examples and examples of the present disclosure.

Fig. 2 shows magnetic flux densities (Y-axis) according to coercive force (X-axis) measured in comparative example 1, and example 2, respectively. Referring to fig. 2, it was confirmed that the characteristics of the sintered magnets were improved in examples 1 and 2 as compared to comparative example 1. Further, the case of sintering using a metal alloy powder as a sintering agent (example 2) has improved characteristics of a sintered magnet, compared to the case of mixing and sintering powders of materials corresponding to respective sintering component elements (example 1). When the amount of increase in the coercive force of example 2 was converted into a percentage compared with example 1, an improvement of about 10% to 20% could be confirmed. That is, a significant increase in coercive force can be obtained depending on the shape change of the sintering agent.

Fig. 3 shows the magnetic flux density (Y-axis) according to the coercive force (X-axis) measured in comparative example 2, example 3, and example 4, respectively. Referring to fig. 3, it can be confirmed that the characteristics of the sintered magnets are improved in examples 3 and 4 as compared to comparative example 2. Further, the case of sintering using a metal alloy powder as a sintering agent (example 4) has improved characteristics of a sintered magnet, compared to the case of mixing and sintering powders of materials corresponding to respective sintering component elements (example 3).

Fig. 4 shows the magnetic flux density (Y-axis) according to the coercive force (X-axis) measured in comparative example 2, example 4, example 5, and example 6, respectively. Referring to fig. 4, it can be confirmed that the characteristics of the sintered magnets are improved in examples 4, 5 and 6 as compared to comparative example 2. Further, when sintering is performed using a metal alloy powder as a sintering agent, it is confirmed that the characteristics of the sintered magnet are improved even if the type of rare earth metal contained in the metal alloy is changed. In particular, it was confirmed that the characteristics of the sintered magnet were most improved when Dy among rare earth metals was contained in the metal alloy. Further, in the present embodiment, the sintering agent of the three-phase metal alloy, i.e., the R — Al — Cu (where R is Nd, Pr, Dy, Tb, or Ce) metal alloy has been described, but a quaternary metal alloy to which other metal such as Ga is added may also be applied as an example of modification.

Hereinafter, a case where a quaternary metal alloy is formed in a method of producing a sintered magnet according to one embodiment of the present disclosure will be described. However, the following embodiments correspond to the embodiments for explaining the present disclosure, and the scope of the present disclosure is not limited thereto.

Example 7

A sintered magnet was formed by sintering under substantially the same conditions as in comparative example 1, and then Pr was used_0.7Al_0.2Cu_0.1Ga_0.1The metal alloy powder of (2) as an auxiliary agent for infiltration.

To prepare Pr_0.7Al_0.2Cu_0.1Ga_0.1The metal alloy powder of (4), using the following method for producing a sintering agent. Pr powder, Al powder, Cu powder and liquid Ga were mixed, and the mixture was agglomerated by Cold Isostatic Pressing (CIP). Then, the agglomerated mixture was wrapped in Mo metal foil or Ta metal foil, heated to 300 degrees celsius for 1 hour in an argon (Ar) gas atmosphere, and further heated at 900 degrees celsius to 1050 degrees celsius for another 1 hour. The prepared metal alloy is pulverized to obtain a powder form.

Example 8

Sintering was carried out under substantially the same conditions as in example 7, except that Dy was used_0.7Al_0.2Cu_0.1Ga_0.1The alloy powder used as an auxiliary agent for infiltration to replace Pr_0.7Al_0.2Cu_0.1Ga_0.1The alloy powder of (4).

Fig. 5 and 6 are graphs showing magnetic flux densities (Y-axis) according to coercive force (X-axis) measured before and after using a quaternary metal alloy powder as an adjuvant for infiltration sintering of a magnet. In FIG. 5, to confirm the use of Pr of example 7_0.7Al_0.2Cu_0.1Ga_0.1In which 2% by weight of Pr relative to the sintered magnet is used_0.7Al_0.2Cu_0.1Ga_0.1Is attached to the sintered magnet, infiltration is performed at 900 degrees celsius for about 10 hours under high vacuum, and post heat treatment is performed at about 520 degrees celsius, and the resulting coercive force is shown before and after. FIG. 6 shows Dy using example 8_0.7Al_0.2Cu_0.1Ga_0.1The coercivity level of the magnet infiltrated with the metal alloy powder of (a).

Referring to fig. 5 and 6, it can be confirmed that the coercive force is improved when the quaternary metal alloy powder is used as the infiltration aid.

Although preferred embodiments of the present disclosure have been described in detail above, the scope of the present disclosure is not limited thereto, and various modifications and improvements of the basic concept of the present disclosure, which are defined in the following claims, by those skilled in the art also belong to the scope of the claims.

Description of the reference numerals

100: crucible pot

200: tube furnace

Claims

1. A method for producing a sintered magnet, comprising the steps of:

an R-Fe-B based magnet powder is produced by a reduction-diffusion method,

adding R-Al-Cu powder as a sintering agent to the R-Fe-B based magnet powder to form a mixed powder, and

sintering the mixed powder to form a sintered magnet,

wherein the R-Al-Cu powder is an alloy of R, Al and Cu, and the R is Nd, Pr, Dy, Tb, or Ce.

2. The method for producing a sintered magnet according to claim 1,

further comprising the step of forming an R-Al-Cu powder as the sintering agent,

wherein the step of forming the R-Al-Cu powder comprises the steps of:

mixing RH with water₂The powder, the Al powder and the Cu powder are mixed to form a sintered precursor,

(ii) agglomerating the sintering precursor(s),

increasing the temperature of the agglomerated sintering precursor to form a metal alloy, and

pulverizing the metal alloy to form the sintering agent.

3. The method for producing a sintered magnet according to claim 2,

further comprising the step of including the sintered precursor in a metal foil while increasing the temperature of the agglomerated sintered precursor.

4. The method for producing a sintered magnet according to claim 3,

wherein the step of forming the sintering precursor further comprises the step of mixing liquid Ga.

5. The method for producing a sintered magnet according to claim 3,

wherein the metal foil is Mo or Ta.

6. The method for producing a sintered magnet according to claim 5,

wherein the temperature is increased in an argon atmosphere when the agglomerated sintering precursor is wrapped in the metal foil and the temperature is increased.

7. The method for producing a sintered magnet according to claim 2,

wherein the step of forming the metal alloy further comprises the steps of: the agglomerated sintering precursor is wrapped in a metal foil, the temperature is raised to 900 to 1050 degrees celsius, and then additional heat treatment is performed.

8. The method for producing a sintered magnet according to claim 2,

wherein the step of agglomerating the sintering precursor uses any one of hydraulic compaction, tapping and Cold Isostatic Pressing (CIP).

9. The method for producing a sintered magnet according to claim 1,

further comprising adding NdH to the R-Al-Cu powder as the sintering agent₂And (5) powder preparation.

10. A sintered magnet produced by the production method according to claim 1.